1. Field of the Invention
The present invention relates to an LED device, an LED device array, and a method of driving the LED device array, and more particularly, to an LED device and an LED device array, which enable partial control of emission intensity of an LED light emitting portion and are suitable for use as a light source for electrophotographic (EP) exposure in an LED scanner and an EP exposure device.
2. Description of the Related Art
In recent years, a printer that uses an LED array having an imaging spot pitch of 600 dpi or 1,200 dpi as a light source has been commercialized.
In the LED device array of 1,200 dpi, light emitting points are arranged in line on a semiconductor at a pitch of 21.2 μm and a light emitting point size of about 10 μm. Thus, high-resolution printing is realized by such microspots.
Such LED device array is illustrated in FIG. 10 as an LED array of Japanese Patent Application Laid-Open No. 2005-064104.
In FIG. 10, LEDs are arranged at a 1,200 dpi pitch, and four LEDs form one block.
A first electrode 7c, which is formed on a part of the upper surface of each light emitting portion 1, is connected to an individual one of four wirings 4 via an extraction wiring. A second electrode 3 is shared by four LEDs. The four wirings are connected to the first electrodes of corresponding LEDs of four blocks. Each block includes a bonding pad 6a connected to the second electrode 3 and a bonding pad 6c connected to one of the four wirings.
Through the selection of one of the four wirings functioning as a switch, an arbitrary LED can be caused to emit light.
With this configuration, the number of the bonding pads can be reduced, thereby enabling driving of a high density LED array.
On the other hand, as an LED device array that realizes a higher density, Japanese Patent Application Laid-Open No. 2007-207977 proposes a structure capable of reducing the emission point pitch and reducing the emission size. FIG. 13 illustrates the LED device array.
In FIG. 13, p-type electrodes 304a, 304b, and 304c are arranged on a first surface, and n-type electrodes 305a and 305b are arranged on a second surface on the opposite side across an active layer. Both the electrodes are formed so as not to superimpose their projections.
When the p-type electrode on the first surface and one of the nearest two n-type electrodes on the second surface are energized, the active layer positioned at an intermediate portion between both the electrodes is caused to emit light. In this manner, the emission point pitch and the emission size are reduced.
Note that, the LED device array of FIG. 13 includes a light emitting layer 301, a p-type current diffusion layer 302, an n-type current diffusion layer 303, and light emitting portions 306a, 306b, 306c, and 306d. 
However, the LED device and the LED device array in the related art have the following problem.
For example, in an LED scanner that uses an LED device array as a light source, each LED device forms a single imaging spot on a photosensitive drum, and hence the pixel density in the horizontal scanning direction is determined by the density of LEDs.
A higher pixel density can be realized by an increase in density of the LED devices. However, the size of a drive circuit increases because of an increase in the ratio of the non-emission portions and an increase in number of the LED devices due to reductions in electrode width and emission area of the LED device. As a result, cost increases.